Fairness of a cluster is evaluated in terms of the balance score [1]} as the minimum ratio between two groups.
\(\leavevmode \xbox {resizebox}{\XMLaddatt {width}{0.0pt}balance(C_i)=\min \left(\frac{|\lbrace x \in C_i \mid \psi (x)=0\rbrace |}{|\lbrace x \in C_i \mid \psi (x)=1\rbrace |},\frac{|\lbrace x \in C_i \mid \psi (x)=1\rbrace |}{|\lbrace x \in C_i \mid \psi (x)=0\rbrace |}\right)}\) 
